The present invention relates to a method for fabricating a metal electrode in a semiconductor device; and, more particularly, to a method for fabricating a metal electrode of nickel (Ni), palladium (Pd) or platinum (Pt) with an atomic layer deposition (ALD) technique.
When fabricating a metal electrode by using nickel, palladium or platinum according to the prior art, the metal electrode is formed by a chemical vapor deposition (CVD) technique using a precursor, of which an oxidation state is of +2 or +4, and a reactive gas, such as a hydrogen gas or the like.
Generally, the CVD technique is employed for depositing a film on an exposed surface of a substrate, such as a silicon wafer or the like, and the precursor used at the CVD is a thermo-decomposable and volatile compound. The precursor is contacted on a substrate heated over a decomposition temperature of the precursor. A film composed of metal, metal compound, metal alloy, ceramic, metal oxide and a mixture thereof is formed on a substrate, which depends on selection of precursor and reaction conditions.
A method for fabricating a metal electrode of nickel, palladium or platinum by using CVD, hereinafter, will be described.
When the metal electrode is formed by CVD, a precursor (MX2 or MX4), of which an oxidation state is of +2 or +4, and a reaction gas, such as an oxygen gas, a hydrogen gas or the like, are used. In the precursor MX2 or MX4, M is one of nickel, palladium and platinum and X is an anionic ligand.
When the oxygen gas is used as the reaction gas, the oxygen gas reduces an oxidized metal precursor by a reaction with the metal precursor and reacts with the anionic ligand X to generate by-products. The ligand is a material selected from the group consisting of H2, Cl, Br, I, C1xcx9cC10 alkyl, C2xcx9cC10 alkenyl, C1xcx9cC8 alkoxy, C6xcx9cC12 aryl, xcex2-diketonates, cyclopentadienyl, C1xcx9cC8 alkylcyclopentadienyl and derivatives thereof including halogens therein. Neutral products among the reaction products, which are produced through oxidation and reduction reaction between the oxygen gas and the metal precursor, may be removed with a vacuum pump. However, since it is very difficult to remove the anionic and cationic products, they may be left in the metal electrode as impurities.
Also, The reaction of oxygen and the ligand is not only complex, but also rapidly performed, so that impurities such carbon, hydrogen and oxygen remain in the metal electrode. The remaining impurities are diffused at a post-thermal process so that a characteristic of the metal electrode is degraded.
To solve the above problem, in case of using hydrogen, which is a reductive gas, as a reaction gas, the metal electrode precursor previously undergoes decomposition and then a carbonate is produced so that impurities still remain in the metal electrode because a deposition temperature has to be set over 700xc2x0 in order to activate the hydrogen.
When the metal electrode is used as an top electrode of a capacitor with dielectric layers such as Ta2O5, (Bi,La)4Ti3O12 (BLT), SrBi2Ta2O9 (SBT), SrxBiy(TaiNbj)2O9 (SBTN), BaxSr(1xe2x88x92x)TiO3 (BST), Pb(Zr,Ti)O3 (PZT) and the like, if the H2 gas is supplied at a high temperature as a reaction gas, H2 reduces the dielectric oxide layer so that the desired electrical characteristics cannot be obtained.
Furthermore, when the metal electrode is formed with nickel, palladium or platinum by using CVD, since the metal precursor of a gas state and the reaction gas are simultaneously supplied into the reaction chamber, a decomposition reaction occurs between the reaction gas and the metal precursor. Non-volatile materials, such as carbonate, oxide and the like, are also produced by the above reaction. These non-volatile materials exist in the metal electrode and cause generation of particles, which induce an operation failure.
When a nickel metal electrode is formed by CVD, sizes of nickel particles are about 0.1 xe2x96xa1 to 1.0 xe2x96xa1. If the particles having a size of about 0.1 xe2x96xa1 to 1.0 xe2x96xa1 stick to the dielectric layer formed to a thickness of about 0.03 xe2x96xa1, a serious problem is caused for a step coverage characteristic of the dielectric layer and a dielectric characteristic is deteriorated. In case of a memory device, since an operation failure of a memory cell having these particles is caused, so that the yield is decreased.
It is, therefore, an object of the present invention to provide a method for fabricating a metal electrode capable of removing impurities and particles therein by using an atomic layer deposition (ALD) technique.
In accordance with an aspect of the present invention, there is provided a method for fabricating a semiconductor memory device, comprising the steps of: loading a substrate into a reaction chamber for an atomic layer deposition; injecting an precursor consisting of M and X into the reaction chamber and including an adsorption precursor onto a surface of the substrate, wherein M is one of nickel (Ni), palladium (Pd) and platinum (Pt) and X is ligand,; purging the reaction chamber; injecting a reaction gas into the reaction chamber and forming a metal layer by,reacting the precursor adsorbed on the surface of the substrate with the reaction gas; and purging the reaction chamber.
In accordance with another aspect of the present invention, there is provided a semiconductor memory device comprising: a substrate: and a metal layer formed on the substrate by using an atomic layer deposition, wherein the metal layer is formed by reacting a precursor consisting of M and X with a reaction gas on a surface of the substrate, wherein M is one of nickel (Ni), palladium (Pd) and platinum (pt), and X is ligand.